1. Field of the Invention
The present invention relates to a novel improvement in the method for preparing comenic acid (5-hydroxy-2-carboxy-4-pyrone), and more particularly to an improvement in the process for preparing comenic acid from 2,5-diketo-gluconic acid or its metal salt and for obtaining comenic acid from the resultant reaction mixture, in substantially appreciable yields, greater than that obtained in our co-pending application noted above.
2. Description of the Prior Art
Few reports deal with the preparation of comenic acid. For instance, Aida et al reported that the presence of comenic acid, rubiginic acid and rubiginol was confirmed by the paper chromatography of an incubated solution of 2,5-diketo-gluconic acid with Gluconoacetobacter liquefaciens and a phosphoric buffer. (Aida et al; Bulletin of the Agricultural Chemical Society of Japan 21 30-37 (1957)). Moreover, they reported that comenic acid and other .gamma.-pyrone derivatives were produced by the fermentation of Gluconacetobacter liquefaciens in a medium containing glucose (9.3%), yeast extract (0.8%), and calcium carbonate (2.5%) for ten days. (Aida et al; Bulletin Agricultural Chemical Society, Japan 19, 97 (1955)). The latter fermentation method however, is of no avail for manufacturing comenic acid because of its poor yield (e.g., only 0.5 g. comenic acid is obtained from 100 g. of glucose by the fermentation).
On the hand, the chemical methods have been known. Chemical procedures involve the oxidation of kojic acid of the decarboxylation of meconic acid. These methods are not economical because the starting materials are very expensive.